A superconducting single-photon detector is like a string stretched in the dark. When a single photon hits it, the string momentarily loses its superconductivity, and we hear a click. But until now, the string was always out of tune: the detector performed worse than the material would allow.

The reason is the uneven distribution of current across the detector's width. The current doesn't flow uniformly; it bunches up at the edges, leaving the middle less sensitive. The researchers added superconducting "rails" along the sides and ran extra current through them. These rails redistribute the current across the entire width of the detector, like a comb that smooths tangled hair. As a result, the detector has finally operated at the edge of its physical capabilities.

The effect is striking: false counts (dark counts) dropped by a factor of ten billion. And a detector 20 micrometers wide began catching photons with a wavelength of 4 micrometers at nearly 100 percent efficiency. Previously, such wavelengths required detectors twenty times narrower. This opens the way to making large detectors without sacrificing quality, as if you could stretch the string wider and still have it sound just as pure.

Now superconducting detectors can become truly large and sensitive. This matters for quantum communication, astronomy, and medical imaging.